1. Field of the Invention
This invention relates to the lamination of large glass sheets using plasticized interlayer material without the use of autoclaves. Normally, plasticized polyvinyl butyral, the most common interlayer material available commercially, has a plasticizer content that optimizes certain characteristics of the resulting laminate, such as its resistance to penetration on impact and the uniformity of adhesion of the interlayer to glass. Generally, to little plasticizer causes the interlayer to be too rigid to flow to conform to the glass during lamination. Too much plasticizer causes the interlayer to soften to the extent that it has poor impact resistance.
Plasticized polyvinyl butyral usually has surfaces that are embossed or patterned. When laminating glass to plasticized polyvinyl butyral, the high temperature and pressure applied within an autoclave smoothes out the patterns or embossments on the major surfaces of the sheet of flexible interlayer material and helps promote the lamination of the plasticized polyvinyl butyral to glass. However, the cost of autoclaves is such that for specialty products that presently have a relatively small market, such as large sized glass sheets of the type that are used for laminated sliding doors for patios and laminated closures for glazing in buildings, the size of the orders for such specialty parts is such that other techniques that do not require the use of an autoclave would be preferred.
It has been suggested to immerse the sheets of an assembly to be laminated within a bath containing additional plasticizer in laminar relation to one another in order to effect a lamination without the use of an autoclave. Such techniques have introduced problems, particularly in attempts to laminate glass sheets of sizes involved in patio doors or larger, because immersing all of the sheets forming the laminate within a bath of plasticizer requires the removal of the plasticizer from the outer surfaces of the resulting laminated unit. When glass units are formed by immersing two glass sheets and a sheet of plasticized polyvinyl butyral in a tank containing additional plasticizer, operators working in such a manner find the plasticizer extremely irritating to their skin and have to use gloves in handling the layers of materials to be laminated. It would be beneficial for the glass sheet laminating art to develop a laminating technique that minimizes the need to expose operators to direct contact with plasticizer.
Interlayer sheeting, particularly polyvinyl butyral, is supplied by manufacturers having an optimum plasticizer content that combines sufficient plasticizer to enable the patterned major surfaces to deform readily and bond to adjacent glass sheets under temperature and pressure conditions that prevail in an autoclave and less than the plasticizer content that causes the interlayer sheet to soften unduly and lose its penetration resistance. However, when an interlayer sheet is exposed to excess plasticizer, its plasticizer content increases at a rate that depends on its temperature of exposure. At low temperatures, the rate of plasticizer increase is too slow to provide a commercially feasible low temperature, low pressure laminating process. At higher temperatures of exposure of the interlayer sheet to a plasticizer bath, it becomes difficult to control a low pressure lamination method to avoid increasing the plasticizer content of the interlayer at an excessive rate to a concentration at which the interlayer gets too soft before it forms a secure bond to the glass sheets of the assembly to be laminated.
The glass laminating art was in dire need of a non-autoclave laminating technique that would provide laminated glass products that had both optical and physical properties commensurate with those obtained by laminating interlayer materials having the optimum plasticizer content in an autoclave. The glass laminating art needed a non-autoclave technique that would work well with interlayer material such as sheets of plasticized polyvinyl butyral that have surfaces that are patterned and would produce laminated units having good penetration resistance as well as good adhesion between the glass sheets and the patterned plastic interlayer.
2. Description of Patents of Interest
British Pat. No. 355,604 to Newtex Safety Glass Company discloses a method of making a laminate of a sheet of cellulose acetate between two sheets of glass by laying a sheet of glass into a suitable bath of a resin in the A stage of its manufacture, laying the cellulose acetate sheet on the glass sheet within the bath, laying the second glass sheet over the cellulose acetate sheet within the bath, removing the assembly from the bath, wiping off excess bath composition from the outer faces and removing surplus bath composition from between the laminae by gentle hand pressure. The resulting assembly is placed in a suitable press and pressed at a pressure of 300 pounds per square inch at 90.degree. to 130.degree. C. for 40 minutes. The immersion is alleged to avoid areas of non-adhesion between adjacent layers of the assembly, but requires autoclave pressures, an expensive solution.
U.S. Pat. No. 3,449,184 to Balk eliminates the need for an expensive autoclave to complete the lamination of laminated glass products by completely immersing alternate sheets of glass and interlayer material in a bath of liquid plasticizer material to inundate said sheets in said bath and arranging said sheets in laminar relation to one another while immersed within said bath. Allegedly, this process may be accomplished in anywhere from about one-half to several hours at room temperature but the process may be accelerated by subjecting products being cured to heat. Unfortunately, the quality of articles so produced does not meet the commercial standards required for present day products.
When, as in both these patents, all the layers of the assembly to be laminated are immersed in a bath of plasticizer, it is necessary to remove the excess plasticizer from the external surfaces of the laminated unit that results. Such a removal step is messy, time-consuming and expensive. It would be desirable to develop a method that avoids such a step.